Differential CPP GMR head

ABSTRACT

A differential current-perpendicular-to-the-plane (CPP) giant magnetoresistive (GMR) sensor is provided having nonmagnetic high conductivity leads to achieve low lead resistance. The differential CPP GMR sensor comprises a first spin valve (SV) sensor, a second SV sensor and a metal gap layer disposed between the first and the second SV sensors. Because of the differential operation of the CPP GMR sensor of this invention, there is no need for shield layers to screen the sensor from stray magnetic fields. The shield layers are replaced with thick nonmagnetic lead layers having high conductivity to reduce the lead resistance of the sensor. Suitable materials for forming the leads include tungsten (W), gold (Au), rhodium (Rh), copper (Cu) and tantalum (Ta) because of their conductivity properties and because they are robust with respect to corrosion and smearing.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates in general to magnetic transducers forreading information signals from a magnetic medium and, in particular,to a differential current-perpendicular-to-the-plane giantmagnetoresistance sensor with improved non-magnetic high conductivityleads.

[0003] 2. Description of Related Art

[0004] Computers often include auxiliary memory storage devices havingmedia on which data can be written and from which data can be read forlater use. A direct access storage device (disk drive) incorporatingrotating magnetic disks is commonly used for storing data in magneticform on the disk surfaces. Data is recorded on concentric, radiallyspaced tracks on the disk surfaces. Magnetic heads including readsensors are then used to read data from the tracks on the disk surfaces.

[0005] In high capacity disk drives, magnetoresistive (MR) read sensors,commonly referred to as MR sensors, are the prevailing read sensorsbecause of their capability to read data from a surface of a disk atgreater track and linear densities than thin film inductive heads. An MRsensor detects a magnetic field through the change in the resistance ofits MR sensing layer (also referred to as an “MR element”) as a functionof the strength and direction of the magnetic flux being sensed by theMR layer.

[0006] The conventional MR sensor operates on the basis of theanisotropic magnetoresistive (AMR) effect in which an MR elementresistance varies as the square of the cosine of the angle between themagnetization in the MR element and the direction of sense currentflowing through the MR element. Recorded data can be read from amagnetic medium because the external magnetic field from the recordedmagnetic medium (the signal field) causes a change in the direction ofmagnetization in the MR element, which in turn causes a change inresistance in the MR element and a corresponding change in the sensedcurrent or voltage.

[0007] Another type of MR sensor is the giant magnetoresistance (GMR)sensor manifesting the GMR effect. In GMR sensors, the resistance of theMR sensing layer varies as a function of the spin-dependent transmissionof the conduction electrons between magnetic layers separated by anonmagnetic layer (spacer) and the accompanying spin-dependentscattering which takes place at the interface of the magnetic andnonmagnetic layers and within the magnetic layers.

[0008] GMR sensors using only two layers of ferromagnetic material(e.g., Ni—Fe) separated by a layer of nonmagnetic material (e.g.,copper) are generally referred to as spin valve (SV) sensors manifestingthe SV effect.

[0009]FIG. 1 shows an SV sensor 100 comprising end regions 104 and 106separated by a central region 102. A first ferromagnetic layer, referredto as a pinned layer 120, has its magnetization typically fixed (pinned)by exchange coupling with an antiferromagnetic (AFM) layer 125. Themagnetization of a second ferromagnetic layer, referred to as a freelayer 110, is not fixed and is free to rotate in response to themagnetic field from the recorded magnetic medium (the signal field). Thefree layer 110 is separated from the pinned layer 120 by a nonmagnetic,electrically conducting spacer layer 115. Hard bias layers 130 and 135formed in the end regions 104 and 106, respectively, providelongitudinal bias for the free layer 110. Leads 140 and 145 formed onhard bias layers 130 and 135, respectively, provide electricalconnections for sensing the resistance of SV sensor 100. In the SVsensor 100, because the sense current flow between the leads 140 and 145is in the plane of the SV sensor layers, the sensor is known as acurrent-in-plane (CIP) SV sensor. IBM's U.S. Pat. No. 5,206,590 grantedto Dieny et al. discloses a GMR sensor operating on the basis of the SVeffect.

[0010] Another type of spin valve sensor is an antiparallel pinned (AP)spin valve sensor. The AP-pinned spin valve sensor differs from thesimple spin valve sensor in that an AP-pinned structure has multiplethin film layers instead of a single pinned layer. The AP-pinnedstructure has an antiparallel coupling (APC) layer sandwiched betweenfirst and second ferromagnetic pinned layers. The first pinned layer hasits magnetization oriented in a first direction by exchange coupling tothe antiferromagnetic pinning layer. The second pinned layer isimmediately adjacent to the free layer and is antiparallel exchangecoupled with the first pinned layer because of the selected thickness(in the order of 8 OE) of the APC layer between the first and secondpinned layers. Accordingly, the magnetization of the second pinned layeris oriented in a second direction that is antiparallel to the directionof the magnetization of the first pinned layer.

[0011] The AP-pinned structure is preferred over the single pinned layerbecause the magnetizations of the first and second pinned layers of theAP-pinned structure subtractively combine to provide a net magnetizationthat is less than the magnetization of the single pinned layer. Thedirection of the net magnetization is determined by the thicker of thefirst and second pinned layers. A reduced net magnetization equates to areduced demagnetization field from the AP-pinned structure. Since theantiferromagnetic exchange coupling is inversely proportional to the netpinning magnetization, this increases exchange coupling between thefirst pinned layer and the antiferromagnetic pinning layer. An AP-pinnedspin valve sensor is described in commonly assigned U.S. Pat. No.5,465,185 to Heim and Parkin.

[0012] There is a continuing need to increase the MR coefficient andreduce the thickness of GMR sensors. An increase in the spin valveeffect and reduced sensor geometry and reduced sensor geometry equatesto higher bit density (bits/square inch of the rotating magnetic disk)read by the read head.

SUMMARY OF THE INVENTION

[0013] It is an object of the present invention to disclose adifferential current-perpendicular-to-the-plane (CPP) GMR sensor havingnonmagnetic high conductivity leads to achieve low lead resistance.

[0014] It is another object of the present invention to disclose adifferential CPP GMR sensor having an improved delta R/R due to reducedparasitic resistance of the leads.

[0015] In accordance with the principles of the present invention, thereis disclosed a differential CPP GMR sensor comprising a first spin valve(SV) sensor, a second SV sensor and a metal gap layer disposed betweenthe first and the second SV sensors. The differential CPP SV sensor issandwiched between thick first and second lead layers formed ofnonmagnetic high conductivity metals. In a first embodiment, the firstSV sensor comprises an antiparallel (AP)-coupled first pinned layeradjacent to a first free layer and the second SV sensor comprises anAP-coupled second pinned layer adjacent to a second free layer. A metalgap layer is sandwiched between the first and second free layers.Because of the differential operation of the CPP GMR sensor of thisinvention, there is no need for shield layers to screen the sensor fromstray magnetic fields. The shield layers are replaced with thicknonmagnetic lead layers having high conductivity to reduce the leadresistance of the sensor. Suitable materials for forming the leadsinclude tungsten (W), gold (Au), rhodium (Rh), copper (Cu) and tantalum(Ta) because of their conductivity properties and because they arerobust with respect to corrosion and smearing.

[0016] The half-bit length of magnetic data recorded on the magneticmedia is arranged to be equal to the spacing between the first andsecond free layers of the differential CPP GMR sensor. With the half-bitlength equal to the spacing between the free layers, the signalsgenerated by the first and second spin valve sensors add due to the 180°phase difference of the first and second pinned layers. Because of thedifferential operation of this CPP sensor, stray magnetic fields do notgenerate any signal. Therefore, there is no need for ferromagneticshields on either side of the differential CPP sensor of the presentinvention.

[0017] The above as well as additional objects, features, and advantagesof the present invention will become apparent in the following detaileddescription.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] For a fuller understanding of the nature and advantages of thepresent invention, as well as of the preferred mode of use, referenceshould be made to the following detailed description read in conjunctionwith the accompanying drawings. In the following drawings, likereference numerals designate like or similar parts throughout thedrawings.

[0019]FIG. 1 is an air bearing surface view, not to scale, of a priorart SV sensor;

[0020]FIG. 2 is a simplified diagram of a magnetic recording disk drivesystem using the SV sensor of the present invention;

[0021]FIG. 3 is a vertical cross-section view, not to scale, of a“piggyback” read/write magnetic head;

[0022]FIG. 4 is an air bearing surface view, not to scale, of anembodiment of a differential CPP GMR sensor of the present invention;

[0023]FIG. 5 is an air bearing surface view, not to scale, of a secondembodiment of a differential CPP GMR sensor of the present invention;and

[0024]FIG. 6 is an air bearing surface view, not to scale, of a thirdembodiment of a differential CPP GMR sensor of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0025] The following description is the best embodiment presentlycontemplated for carrying out the present invention. This description ismade for the purpose of illustrating the general principles of thepresent invention and is not meant to limit the inventive conceptsclaimed herein.

[0026] Referring now to FIG. 2, there is shown a disk drive 200embodying the present invention. As shown in FIG. 2, at least onerotatable magnetic disk 212 is supported on a spindle 214 and rotated bya disk drive motor 218. The magnetic recording media on each disk is inthe form of an annular pattern of concentric data tracks (not shown) onthe disk 212.

[0027] At least one slider 213 is positioned on the disk 212, eachslider 213 supporting one or more magnetic read/write heads 221 wherethe head 221 incorporates the SV sensor of the present invention. As thedisks rotate, the slider 213 is moved radially in and out over the disksurface 222 so that the heads 221 may access different portions of thedisk where desired data is recorded. Each slider 213 is attached to anactuator arm 219 by means of a suspension 215. The suspension 215provides a slight spring force which biases the slider 213 against thedisk surface 222. Each actuator arm 219 is attached to an actuator 227.The actuator as shown in FIG. 2 may be a voice coil motor (VCM). The VCMcomprises a coil movable within a fixed magnetic field, the directionand speed of the coil movements being controlled by the motor currentsignals supplied by a controller 229.

[0028] During operation of the disk storage system, the rotation of thedisk 212 generates an air bearing between the slider 213 (the surface ofthe slider 213 which includes the head 321 and faces the surface of thedisk 212 is referred to as an air bearing surface (ABS)) and the disksurface 222 which exerts an upward force or lift on the slider. The airbearing thus counter-balances the slight spring force of the suspension215 and supports the slider 213 off and slightly above the disk surfaceby a small, substantially constant spacing during normal operation.

[0029] The various components of the disk storage system are controlledin operation by control signals generated by the control unit 229, suchas access control signals and internal clock signals. Typically, thecontrol unit 229 comprises logic control circuits, storage chips and amicroprocessor. The control unit 229 generates control signals tocontrol various system operations such as drive motor control signals online 223 and head position and seek control signals on line 228. Thecontrol signals on line 228 provide the desired current profiles tooptimally move and position the slider 213 to the desired data track onthe disk 212. Read and write signals are communicated to and from theread/write heads 221 by means of the recording channel 225. Recordingchannel 225 may be a partial response maximum likelihood (PRML) channelor a peak detect channel. The design and implementation of both channelsare well known in the art and to persons skilled in the art. In thepreferred embodiment, recording channel 225 is a PRML channel.

[0030] The above description of a typical magnetic disk storage system,and the accompanying illustration of FIG. 2 are for representationpurposes only. It should be apparent that disk storage systems maycontain a large number of disks and actuator arms, and each actuator armmay support a number of sliders.

[0031]FIG. 3 is a side cross-sectional elevation view of a “piggyback”magnetic read/write head 300, which includes a write head portion 302and a read head portion 304, the read head portion employing adifferential CPP GMR sensor 306 according to the present invention. Thesensor 306 is sandwiched between nonmagnetic conductive first and secondlead layers 312 and 314. First and second nonmagnetic insulative layers308 and 310 separate the first and second lead layers in the region awayfrom the sensor located at the ABS. In response to external magneticfields, the resistance of the sensor 306 changes. A sense current Isconducted through the sensor causes these resistance changes to bemanifested as potential changes. These potential changes are thenprocessed as readback signals by the processing circuitry of the datarecording channel 246 shown in FIG. 2.

[0032] The write head portion 302 of the magnetic read/write head 300includes a coil layer 316 sandwiched between first and second insulationlayers 318 and 320. A third insulation layer 322 may be employed forplanarizing the head to eliminate ripples in the second insulation layer320 caused by the coil layer 316. The first, second and third insulationlayers are referred to in the art as an insulation stack. The coil layer316 and the first, second and third insulation layers 38, 320 and 322are sandwiched between first and second pole piece layers 324 and 326.The first and second pole piece layers 324 and 326 are magneticallycoupled at a back gap 328 and have first and second pole tips 330 and332 which are separated by a write gap layer 334 at the ABS 340. Aninsulation layer 336 is located between the second shield layer 314 andthe first pole piece layer 324. Since the second shield layer 314 andthe first pole piece layer 324 are separate layers this read/write headis known as a “piggyback” head.

FIRST EXAMPLE

[0033]FIG. 4 depicts an air bearing surface (ABS) view, not to scale, ofa differential CPP GMR sensor 400 according to a first embodiment of thepresent invention. The sensor 400 comprises end regions 402 and 404separated from each other by a central region 406. The active region ofthe CPP sensor comprises a first SV sensor 410 and a second SV sensor412 formed in the central region 406. The first and second SV sensorsare separated by a metal gap layer 414. The first SV sensor 410 isformed on a seed layer 416 deposited on a first lead layer L1 418 in thecentral region 406. The seed layer 416 a nonmagnetic metal layerdeposited to modify the crystallographic texture or grain size ofsubsequent layers. The first lead layer 418 is a layer of nonmagnetichighly conductive metal such as tungsten (W), or alternatively gold(Au), rhodium (Rh), copper (Cu) or tantalum (Ta) deposited on asubstrate 408 and extending over the central region 406 and end regions402 and 404. Alternatively, the first lead layer 418 may comprise amultilayer of two or more layers, each layer being formed from any ofthe above listed conductive metals. For example the first lead layer maycomprise a bilayer formed of a Ta layer and a Au layer or a bilayerformed of a Ta layer and a Rh layer. The substrate 408 can be anysuitable substance including glass, semiconductor material, or a ceramicsubstance such as alumina (Al₂O₃).

[0034] The first SV sensor 410 comprises a first pinned layer 422 overthe seed layer 416 and a ferromagnetic first free layer 424 depositedover the first pinned layer. The first pinned layer 422 is an AP-coupledlayer comprising a first ferromagnetic (FM1) layer 426 adjacent to theseed layer 416, a second ferromagnetic (FM2) layer 428 and anantiparallel coupling (APC) layer 427 sandwiched between the FM1 and FM2layers 426 and 428. The APC layer 427 is formed of a nonmagneticmaterial, preferably ruthenium (Ru), that allows the FM1 and FM2 layers426 and 428 to be strongly coupled together antiferromagnetically.

[0035] The second SV sensor 412 comprises a ferromagnetic second freelayer 430 deposited over the metal gap layer 414 and a second pinnedlayer 424 deposited over the second free layer. The second pinned layer424 is an AP-coupled layer comprising a third ferromagnetic (FM3) layer432 adjacent to the second free layer 430, a fourth ferromagnetic (FM4)layer 434 and an antiparallel coupling (APC) layer 433 sandwichedbetween the FM3 and FM4 layers 432 and 434. The APC layer 433 is formedof a nonmagnetic material, preferably ruthenium (Ru), that allows theFM3 and FM4 layers 432 and 434 to be strongly coupled togetherantiferromagnetically. A cap layer 436 is deposited over the secondpinned layer 424.

[0036] Insulator layers 440 and 442 of electrically insulating materialsuch as aluminum oxide are formed in the end regions 402 and 404,respectively, on the first lead layer 418 and in abutting contact withthe CPP sensor layers in the central region 406. A second lead layer L2420 of nonmagnetic highly conductive metal such as tungsten (W), oralternatively gold (Au), rhodium (Rh), copper (Cu) or tantalum (Ta), isdeposited over the cap layer 436 in the central region 406 and over theinsulator layers 440 and 442 in the end regions 402 and 404.Alternatively, the second lead layer 420 may comprise a multilayer oftwo or more layers, each layer being formed from any of the above listedconductive metals. For example, the first lead layer may comprise abilayer formed of a Ta layer and a Au layer or a bilayer formed of a Talayer and a Rh layer.

[0037] If longitudinal stabilization of the magnetic domain states ofthe first and second free layers 424 and 430 is desired, hard biaslayers may be provided in the end regions 402 and 404 as is known in theart. IBM's U.S. Pat. No. 5,720,410 granted to Fontana et al. describessuch a longitudinal biasing method.

[0038] The first and second lead layers 418 and 420 provide electricalconnections for the flow of a sensing current Is from a current source450 to the CPP sensor 400. A signal detector 460 which is electricallyconnected to the first and second lead layers 418 and 420 senses thechange in resistance due to changes induced in the first and second freelayers 424 and 430, respectively, by the external magnetic field (e.g.,field generated by a data bit stored on a disk). The external magneticfield acts to rotate the direction of magnetization of the first andsecond free layers relative to the direction of magnetization of thefirst and second pinned layers 422 and 424, respectively, which arepreferably pinned perpendicular to the ABS. The signal detector 460preferably comprises a partial response maximum likelihood (PRML)recording channel for processing the signal detected by the MTJ sensor400. Alternatively, a peak detect channel or a maximum likelihoodchannel (e.g., 1.7 ML) may be used. The design and implementation of theaforementioned channels are known to those skilled in the art. Thesignal detector 460 also includes other supporting circuitries such as apreamplifier (electrically placed between the sensor and the channel)for conditioning the sensed resistance changes as is known to thoseskilled in the art.

[0039] The sensor 400 may be fabricated in a magnetron sputtering or anion beam sputtering system to sequentially deposit the multilayerstructure shown in FIG. 4. The first lead layer 418 of tungsten (W), oralternatively gold (Au), rhodium (Rh), copper (Cu), tantalum (Ta) orcombinations of these materials, having a thickness in the range of500-2000 Å is deposited on the substrate 408. After deposition of thefirst lead layer a chemical/mechanical polish (CMP) is carried out toprovide a smooth surface for deposition of the layer structure of theCPP SV sensor. For the best CMP results, the use of tungsten to form thefirst lead layer is preferred. The seed layer 416, the first SV sensor410, the metal gap layer 414 and the second SV sensor 412 aresequentially deposited over the first lead layer 418 in the presence ofa longitudinal or transverse magnetic field of about 40 Oe to orient theeasy axis of all the ferromagnetic layers. The seed layer 416 formed ofa nonmagnetic metal, preferably tantalum (Ta), having a thickness ofabout 30 Å is deposited on the first lead layer 418. The FM1 layer 426formed of Ni—Fe having a thickness in the range of 20-50 Å is depositedon the seed layer 416. The APC layer 427 preferably formed of ruthenium(Ru) having a thickness of about 6 Å is deposited on the FM1 layer 426.The FM2 layer 428 formed of Ni—Fe having a thickness in the range of20-50 Å is deposited on the APC layer 427. The thickness of the FM1layer 426 is chosen to be greater than the thickness of the FM2 layer428 so that magnetization 443 (shown as the head of an arrow pointingout of the plane of the paper) of the FM1 layer 426 is greater than themagnetization 444 (shown as the tail of an arrow pointing into the planeof the paper) of the FM2 layer 428. As a result, the direction of thenet magnetization of the AP-coupled first pinned layer 422 has the samedirection as the magnetization 443 of the FM1 layer 426. The first freelayer 424 formed of Ni—Fe having a thickness of 20-40 Å is deposited onthe FM2 layer 428. Alternatively, the free layer 428 may be formed of alaminated multilayer comprising a ferromagnetic interface layer formedof cobalt (Co) having a thickness of about 5 Å deposited on the FM1layer 426 and a ferromagnetic layer formed of Ni—Fe having a thicknessof 20-30 Å deposited on the interface layer.

[0040] The metal gap layer 414 formed of a nonmagnetic metal isdeposited over the first free layer 424. The metal gap layer provides aread gap separating the free layers of the first and second SV sensors410 and 412 of the differential CPP sensor 400. With the differentialsensor the recorded magnetic half-bit length is arranged to equal thespacing between the first and second free layers 424 and 430. Themagnetization directions 425 and 431 of first and second free layers 424and 430, respectively, are arranged to have the same direction, eitherto the right as shown in FIG. 4 or, alternatively, to the left. Infuture high density technology applications the metal gap layer willhave a thickness less than 500 Å.

[0041] The second free layer 430 formed of Ni—Fe having a thickness ofabout 20-40 Å is deposited on the metal gap layer 414. Alternatively,the free layer 430 may be formed of a laminated multilayer comprising aferromagnetic layer formed of Ni—Fe having a thickness of 20-30 Ådeposited on the metal gap layer 414 and a ferromagnetic interface layerformed of cobalt (Co) having a thickness of about 5 Å deposited on theferromagnetic layer of Ni—Fe. The FM3 layer 432 formed of Ni—Fe having athickness in the range of 20-50 Å is deposited on the second free layer432. The APC layer 433 preferably formed of ruthenium (Ru) having athickness of about 6 Å is deposited on the FM3 layer 432. The FM4 layer434 formed of Ni—Fe having a thickness in the range of 20-50 Å isdeposited on the APC layer 433. The thickness of the FM3 layer 432 ischosen to be greater than the thickness of the FM4 layer 434 so thatmagnetization 445 (shown as the head of an arrow pointing out of theplane of the paper) of the FM3 layer 432 is greater than themagnetization 446 (shown as the tail of an arrow pointing into the planeof the paper) of the FM4 layer 434. As a result, the direction of thenet magnetization of the AP-coupled first pinned layer 422 has the samedirection as the magnetization 445 of the FM3 layer 432. A cap layer 436of tungsten having a thickness of about 30 Å, formed on the FM4 layer434 completes the central region 406 of the CPP sensor 400. The secondlead layer 420 of tungsten (W), or alternatively gold (Au), rhodium(Rh), copper (Cu), tantalum (Ta) or combinations of these materials,having a thickness in the range of 500-2000 Å is deposited over the caplayer 436 in the central region 406 and over the insulation layers 440and 442 in the end regions 402 and 404.

[0042] An advantage of the differential CPP GMR sensor 400 of thepresent invention is that because of the differential operation of thesensor ferromagnetic shields are not required to prevent stray magneticfields from causing spurious signals. Elimination of the need forshields allows the use of thick high conductivity leads, L1 and L2, toachieve low lead resistance. The low lead resistance provides higherdelta R/R for the sensor because parasitic resistance (resistance notcontributing to delta R) is lowered.

[0043] Another advantage of the differential CPP sensor 400 of thepresent invention is that the first and second pinned layers 422 and 424of the first and second SV sensors 410 and 412, respectively, arearranged to be 180° out of phase to provide signal addition forperpendicular or longitudinal transitions where the half-bit length isset equal to the thickness of the metal gap layer 414 (read gap). Inorder to accomplish this phase relationship of the pinned layers, thethicknesses of ferromagnetic layers FM1, FM2, FM3 and FM4 are selectedso that FM2 and FM3 become 180° out of phase during a reset process.This phase relationship may be achieved by choosing the magneticthickness of FM1 to be greater than the thickness of FM2 and themagnetic thickness of FM3 to be greater than the thickness of FM4.Alternatively, the thickness of FM2 may be chosen to be greater than thethickness of FM1 and the thickness of FM4 may be chosen to be thickerthan the thickness of FM3. The magnetic anisotropy differences betweenFM1, FM2, FM3 and FM4 may also be used to achieve the desired magneticorientation of these layers.

SECOND EXAMPLE

[0044]FIG. 5 shows an air bearing surface (ABS) view, not to scale, of adifferential CPP sensor 500 according to another embodiment of thepresent invention. The CPP SV sensor 500 differs from the CPP SV sensor400 shown in FIG. 4 in having first and second SV sensors 510 and 512comprising simple pinned layers 518 and 520 with first and secondantiferromagnetic (AFM) pinning layers 514 and 516, respectively,instead of the self-pinned AP-coupled layers 422 and 424 of the SVsensor 400. The first AFM layer 514 of Pt—Mn or Ir—Mn having a thicknessin the range of 50-200 Å is deposited over the seed layer 416. The firstpinned layer 518 of Co—Fe having a thickness in the range of 20-40 Å isdeposited over the first AFM layer. The first free layer 424, metal gaplayer 414 and second free layer 430 are sequentially deposited over thefirst pinned layer 518. The second pinned layer 520 of Co—Fe having athickness in the range of 20-40 Å is deposited over the second freelayer and the second AFM layer 516 of Pt—Mn or Ir—Mn having a thicknessin the range of 50-200 Å is deposited over the second pinned layer 520.The cap layer 436 is deposited over the second AFM layer 516.

[0045] The first AFM layer 514 is set at elevated temperature in thepresence of a strong magnetic field, as is known to the art, to pin thedirection of the magnetization 519 (shown as the head of an arrowpointing out of the plane of the paper) of the first pinned layer 518perpendicular to the ABS. The second AFM layer 516 is similarly set topin the direction of the magnetization 521 (shown as the tail of anarrow pointing into the plane of the paper) of the second pinned layer520 in an opposite direction to the magnetization 519 of the firstpinned layer 518. Alternatively, the first pinned layer 518 may bepinned so that the magnetization 519 is directed into the plane of thepaper and the second pinned layer 520 may be pinned so that themagnetization 521 is directed out of the plane of the paper. With thehalf-bit length equal to the spacing between the free layers, thesignals generated by the first and second spin valve sensors of thedifferential CPP sensor 500 add due to the 180° phase difference of themagnetizations of the first and second pinned layers. The setting of thefirst and second AFM layers 514 and 516 180° out of phase may requirethe use of different AFM materials for each layer and setting proceduresknown in the art.

THIRD EXAMPLE

[0046]FIG. 6 shows an air bearing surface (ABS) view, not to scale, of adifferential CPP sensor 600 according to another embodiment of thepresent invention. The CPP SV sensor 600 differs from the CPP SV sensor400 shown in FIG. 4 in having a first SV sensor 610 comprising aself-pinned AP-coupled first pinned layer 614 and a second SV sensor 612comprising a simple pinned layer 620 with an antiferromagnetic (AFM)pinning layer 616 instead of the two self-pinned AP-coupled layers 422and 424 of the SV sensor 400. The SV sensor 612 having a simple pinnedlayer and an AFM pinning layer is preferably the top sensor in the stackforming the differential CPP sensor 600 but, alternatively, may beconfigured as the bottom sensor of the differential CPP sensor. Thefirst SV sensor 610 comprising first pinned layer 614 and first freelayer 424 is the same as first SV sensor 410 of CPP sensor 400. Thesecond pinned layer 620 of the second sensor 612 is formed of Co—Fehaving a thickness in the range of 20-40 Å deposited over the secondfree layer 430. The AFM layer 616 of Pt—Mn or Ir—Mn having a thicknessin the range of 50-200 Å is deposited over the second pinned layer 620.The cap layer 436 is deposited over the AFM layer 616.

[0047] The AFM layer 616 is set at elevated temperature in the presenceof a strong magnetic field, as is known to the art, to pin the directionof the magnetization 621 (shown as the head of an arrow pointing out ofthe plane of the paper) of the second pinned layer 620 perpendicular tothe ABS and in an opposite direction to the magnetization 444 of the FM2layer 428 of the first pinned layer 614. Alternatively, the FM2 layer428 may be pinned so that the magnetization 444 is directed into theplane of the paper and the second pinned layer 620 may be pinned so thatthe magnetization 621 is directed out of the plane of the paper. Withthe half-bit length equal to the spacing between the free layers, thesignals generated by the first and second spin valve sensors of thedifferential CPP sensor 600 add due to the 180° phase difference of themagnetizations of the FM2 layer 428 and the second pinned layer 620.

[0048] While the present invention has been particularly shown anddescribed with reference to the preferred embodiments, it will beunderstood to those skilled in the art that various changes in form anddetail may be made without departing from the spirit, scope and teachingof the invention. Accordingly, the disclosed invention is to beconsidered merely as illustrative and limited only as specified in theappended claims.

I claim:
 1. A differential giant magnetoresistive (GMR) sensor,comprising: a first spin valve (SV) sensor, comprising: a first pinnedlayer, including: a first ferromagnetic (FM1) layer; a secondferromagnetic (FM2) layer; an antiparallel coupling (APC) layer disposedbetween the FM1 and FM2 layers; and a first free layer adjacent to theFM2 layer on a side opposite the APC layer; a second spin valve (SV)sensor, comprising: a second pinned layer, including: a thirdferromagnetic (FM3) layer; a fourth ferromagnetic (FM4) layer; anantiparallel coupling (APC) layer disposed between the FM3 and FM4layers; and a second free layer adjacent to the FM3 layer on a sideopposite the APC layer; a metal gap layer disposed between the first andsecond free layers; and wherein the first and second SV sensors and themetal gap layer are disposed between nonmagnetic first and second leadlayers.
 2. The differential GMR sensor recited in claim 1 wherein thefirst and second lead layers are chosen from a group of materialsconsisting of tungsten (W), gold (Au), rhodium (Rh), copper (Cu),tantalum (Ta) and their combinations.
 3. The differential GMR sensorrecited in claim 1 wherein the metal gap layer provides a read gapseparating the first and second free layers by a spacing equal to therecorded magnetic half-bit length.
 4. The differential GMR sensorrecited in claim 1 wherein the magnetizations of the FM2 and FM3 layersare oppositely directed.
 5. A differential giant magnetoresistive (GMR)sensor, comprising: a first spin valve (SV) sensor, comprising: a firstantiferromagnetic layer; a first free layer; and a first pinned layerdisposed between the first antiferromagnetic layer and the first freelayer; a second spin valve (SV) sensor, comprising: a secondantiferromagnetic layer; a second free layer; and a second pinned layerdisposed between the second antiferromagnetic layer and the second freelayer; a metal gap layer disposed between the first and second freelayers; and wherein the first and second SV sensors and the metal gaplayer are disposed between nonmagnetic first and second lead layers. 6.The differential GMR sensor recited in claim 5 wherein the first andsecond lead layers are chosen from a group of materials consisting oftungsten (W), gold (Au), rhodium (Rh), copper (Cu), tantalum (Ta) andtheir combinations.
 7. The differential GMR sensor recited in claim 5wherein the metal gap layer provides a read gap separating the first andsecond free layers by a spacing equal to the recorded magnetic half-bitlength.
 8. The differential GMR sensor recited in claim 5 wherein themagnetizations of the first and second pinned layers are oppositelydirected.
 9. A differential giant magnetoresistive (GMR) sensor,comprising: a first spin valve (SV) sensor, comprising: a first pinnedlayer, including: a first ferromagnetic (FM1) layer; a secondferromagnetic (FM2) layer; an antiparallel coupling (APC) layer disposedbetween the FM1 and FM2 layers; and a first free layer adjacent to theFM2 layer on a side opposite the APC layer; a second spin valve (SV)sensor, comprising: an antiferromagnetic layer; a second free layer; asecond pinned layer disposed between the antiferromagnetic layer and thesecond free layer; a metal gap layer disposed between the first andsecond free layers; and wherein the first and second SV sensors and themetal gap layer are disposed between nonmagnetic first and second leadlayers.
 10. The differential GMR sensor recited in claim 9 wherein thefirst and second lead layers are chosen from a group of materialsconsisting of tungsten (W), gold (Au), rhodium (Rh), copper (Cu),tantalum (Ta) and their combinations.
 11. The differential GMR sensorrecited in claim 9 wherein the metal gap layer provides a read gapseparating the first and second free layers by a spacing equal to therecorded magnetic half-bit length.
 12. The differential GMR sensorrecited in claim 9 wherein the magnetizations of the first and secondpinned layers are oppositely directed.
 13. A magnetic read/write headcomprising: a write head including: at least one coil layer and aninsulation stack, the coil layer being embedded in the insulation stack;first and second pole piece layers connected at a back gap and havingpole tips with edges forming a portion of an air bearing surface (ABS);the insulation stack being sandwiched between the first and second polepiece layers; and a write gap layer sandwiched between the pole tips ofthe first and second pole piece layers and forming a portion of the ABS;a read head including: a differential giant magnetoresistance (GMR)sensor, the GMR sensor being sandwiched between first and second leadlayers, the GMR sensor comprising: a first spin valve (SV) sensor,comprising: a first pinned layer, including: a first ferromagnetic (FM1)layer; a second ferromagnetic (FM2) layer; an antiparallel coupling(APC) layer disposed between the FM1 and FM2 layers; and a first freelayer adjacent to the FM2 layer on a side opposite the APC layer; asecond spin valve (SV) sensor, comprising: a second pinned layer,including: a third ferromagnetic (FM3) layer; a fourth ferromagnetic(FM4) layer; an antiparallel coupling (APC) layer disposed between theFM3 and FM4 layers; and a second free layer adjacent to the FM3 layer ona side opposite the APC layer; a metal gap layer disposed between thefirst and second free layers; and wherein the first and second SVsensors and the metal gap layer are disposed between nonmagnetic firstand second lead layers; and an insulation layer disposed between thesecond lead layer of the read head and the first pole piece layer of thewrite head.
 14. The magnetic read/write head recited in claim 13 whereinthe first and second lead layers are chosen from a group of materialsconsisting of tungsten (W), gold (Au), rhodium (Rh), copper (Cu),tantalum (Ta) and their combinations.
 15. The magnetic read/write headrecited in claim 13 wherein the metal gap layer provides a read gapseparating the first and second free layers by a spacing equal to therecorded magnetic half-bit length.
 16. The magnetic read/write headrecited in claim 13 wherein the magnetizations of the first and secondpinned layers are oppositely directed.
 17. A magnetic read/write headcomprising: a write head including: at least one coil layer and aninsulation stack, the coil layer being embedded in the insulation stack;first and second pole piece layers connected at a back gap and havingpole tips with edges forming a portion of an air bearing surface (ABS);the insulation stack being sandwiched between the first and second polepiece layers; and a write gap layer sandwiched between the pole tips ofthe first and second pole piece layers and forming a portion of the ABS;a read head including: a differential giant magnetoresistance (GMR)sensor, the GMR sensor being sandwiched between first and second leadlayers, the GMR sensor comprising: a first spin valve (SV) sensor,comprising: a first antiferromagnetic layer; a first free layer; and afirst pinned layer disposed between the first antiferromagnetic layerand the first free layer; a second spin valve (SV) sensor, comprising: asecond antiferromagnetic layer; a second free layer; and a second pinnedlayer disposed between the second antiferromagnetic layer and the secondfree layer; a metal gap layer disposed between the first and second freelayers; and wherein the first and second SV sensors and the metal gaplayer are disposed between nonmagnetic first and second lead layers; andan insulation layer disposed between the second lead layer of the readhead and the first pole piece layer of the write head.
 18. The magneticread/write head recited in claim 17 wherein the first and second leadlayers are chosen from a group of materials consisting of tungsten (W),gold (Au), rhodium (Rh), copper (Cu), tantalum (Ta) and theircombinations.
 19. The magnetic read/write head recited in claim 17wherein the metal gap layer provides a read gap separating the first andsecond free layers by a spacing equal to the recorded magnetic half-bitlength.
 20. The magnetic read/write head recited in claim 17 wherein themagnetizations of the first and second pinned layers are oppositelydirected.
 21. A magnetic read/write head comprising: a write headincluding: at least one coil layer and an insulation stack, the coillayer being embedded in the insulation stack; first and second polepiece layers connected at a back gap and having pole tips with edgesforming a portion of an air bearing surface (ABS); the insulation stackbeing sandwiched between the first and second pole piece layers; and awrite gap layer sandwiched between the pole tips of the first and secondpole piece layers and forming a portion of the ABS; a read headincluding: a differential giant magnetoresistance (GMR) sensor, the GMRsensor being sandwiched between first and second lead layers, the GMRsensor comprising: a first spin valve (SV) sensor, comprising: a firstpinned layer, including: a first ferromagnetic (FM1) layer; a secondferromagnetic (FM2) layer; an antiparallel coupling (APC) layer disposedbetween the FM1 and FM2 layers; and a first free layer adjacent to theFM2 layer on a side opposite the APC layer; a second spin valve (SV)sensor, comprising: an antiferromagnetic layer; a second free layer; asecond pinned layer disposed between the antiferromagnetic layer and thesecond free layer; a metal gap layer disposed between the first andsecond free layers; and wherein the first and second SV sensors and themetal gap layer are disposed between nonmagnetic first and second leadlayers; and an insulation layer disposed between the second lead layerof the read head and the first pole piece layer of the write head. 22.The magnetic read/write head recited in claim 21 wherein the first andsecond lead layers are chosen from a group of materials consisting oftungsten (W), gold (Au), rhodium (Rh), copper (Cu), tantalum (Ta) andtheir combinations.
 23. The magnetic read/write head recited in claim 21wherein the metal gap layer provides a read gap separating the first andsecond free layers by a spacing equal to the recorded magnetic half-bitlength.
 24. The magnetic read/write head recited in claim 21 wherein themagnetizations of the first and second pinned layers are oppositelydirected.
 25. A disk drive system comprising: a magnetic recording disk;a magnetic read/write head for magnetically recording data on themagnetic recording disk and for sensing magnetically recorded data onthe magnetic recording disk, said magnetic read/write head comprising: awrite head including: at least one coil layer and an insulation stack,the coil layer being embedded in the insulation stack; first and secondpole piece layers connected at a back gap and having pole tips withedges forming a portion of an air bearing surface (ABS); the insulationstack being sandwiched between the first and second pole piece layers;and a write gap layer sandwiched between the pole tips of the first andsecond pole piece layers and forming a portion of the ABS; a read headincluding: a differential giant magnetoresistance (GMR) sensor, the GMRsensor being sandwiched between first and second lead layers, the GMRsensor comprising: a first spin valve (SV) sensor, comprising: a firstpinned layer, including: a first ferromagnetic (FM1) layer; a secondferromagnetic (FM2) layer; an antiparallel coupling (APC) layer disposedbetween the FM1 and FM2 layers; and a first free layer adjacent to theFM2 layer on a side opposite the APC layer; a second spin valve (SV)sensor, comprising: a second pinned layer, including: a thirdferromagnetic (FM3) layer; a fourth ferromagnetic (FM4) layer; anantiparallel coupling (APC) layer disposed between the FM3 and FM4layers; and a second free layer adjacent to the FM3 layer on a sideopposite the APC layer; a metal gap layer disposed between the first andsecond free layers; and wherein the first and second SV sensors and themetal gap layer are disposed between nonmagnetic first and second leadlayers; and an insulation layer disposed between the second read gaplayer of the read head and the first pole piece layer of the write head;and an actuator for moving said magnetic read/write head across themagnetic disk so that the read/write head may access different regionsof the magnetic recording disk; and a recording channel coupledelectrically to the write head for magnetically recording data on themagnetic recording disk and to the GMR sensor of the read head fordetecting changes in resistance of the GMR sensor in response tomagnetic fields from the magnetically recorded data.